This invention relates to a variable capacity compressor mainly adapted for use in an air conditioning system for automotive vehicles, and more particularly to a compressor of this kind which has a widened variable range of delivery quantity or capacity.
A variable capacity vane compressor of this kind has conventionally been proposed, e.g. by U.S. Pat. No. 4,744,732 assigned to the same assignee of the present application, which has a control element arranged in one of side blocks forming a cylinder in cooperation with a cam ring, for rotation in opposite directions in response to the difference between low pressure (or suction pressure) from a suction chamber and control pressure created from discharge pressure within a discharge pressure chamber and the suction pressure, to vary the compression starting timing in two diametrically opposite compression chambers defined between adjacent ones of vanes within the cylinder, thereby varying the delivery quantity or capacity of the compression chambers and hence the compressor.
According to the proposed variable capacity compressor, when the compressor is operating at a low rotational speed and accordingly the suction pressure of refrigerant gas as a compression medium is high, the control pressure is increased so that the control element is rotated against the sum of the suction pressure and the force of a coiled return spring biasing the control element in the direction of reducing the capacity, to thereby advance the compression starting timing, at which the compression chambers and the suction chamber are brought out of communication, and hence increase the capacity of the compressor.
On the other hand, when the rotational speed of the compressor increases and accordingly the suction pressure lowers, the control pressure is decreased so that the control element is rotated by the sum of the suction pressure and the force of the coiled return spring in the opposite directiOn to the above, to thereby retard the compression starting timing and hence decrease the capacity of the compressor.
The control element has diametrically opposite cut-out portions, through which the associated compression chambers and the suction chamber are brought into communication with each other. When each vane passes a downstream end of each cut-out portion with respect to the rotational direction of the rotor, the compression chamber and the suction chamber are brought out of communication from each other to start the compression stroke.
The proposed compressor constructed as above has a limited variable range of capacity such that the lower limit of capacity, i.e. the minimum capacity is 10 percent provided that the upper limit or the maximum capacity is 100 percent. To obtain a wider controllable range of temperature, it is desirable that the variable range of capacity should be widened. However, the maximum angle through which the control element can rotate is no more than 65 to 70 degrees due to structural limitation of the compressor. To obtain a wider variable range of capacity, the minimum capacity has to be reduced to a value as small as possible. However, in the proposed compressor, if the cut-out portion is formed in the control element so that its downstream end is located further downstream with respect to the rotational direction of the rotor so as to obtain a wider variable range of capacity, the timing at which the compression chamber is brought out of communication from the suction chamber is correspondingly retarded to decrease the suction efficiently during the full capacity operation, thereby lowering the maximum capacity of the compressor.
Further, if the minimum capacity is excessively decreased, a required compression ratio for starting the compressor cannot be obtained at the start of the compressor, thereby degrading the startability of the compressor.